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The usage of smart terminals and laptops as well as the proliferation of mobile applications create an enormous amount of data traffic in the mobile networks. Ericsson (2011) predicts that within the next five years (2011-2016), mobile data traffic will grow 10 times as the number of mobile broadband subscriptions increases from 900 Million to almost 5 Billion globally. In fact, people spend most of the time at home and office and the majority of smartphone usage takes place while people are indoors (Smura, 2008). Around 70-80% of the mobile data traffic is generated indoors (Chowdhury & Noll, 2010). However, the radio signals incur significant additional attenuation when they are transmitted from outdoor to indoor environment, due to the building penetration losses. The signal degradation results in poor quality of service in indoor places, and subsequently, macrocell needs to dedicate more radio resources for an indoor connection to compensate the degradation.
Mobile operators have to address the challenges for achieving sufficient coverage, capacity and quality targets under the aforementioned conditions. The traditional macrocell deployment strategy with the installation of more dense cellular sites might meet the requirements, however such deployment is not a cost and energy efficient solution (Katsigiannis & Hämmäinen, 2011). It requires large number of base stations which is accompanied by high investments and operating costs. The latter is further increased due to the power consumption of the radio access network which creates huge energy bills for mobile operators. Besides the economic impact, the increasing power consumption of radio access network has a strong environmental effect due to the growing carbon dioxide (C02) emissions (Fehske, Fettweis, Malmodin, & Biczók, 2011). Consequently, different deployment strategies have to be investigated by mobile operators (Webb, 2009).
Mobile network offloading as a deployment strategy, especially in densely populated areas such as metropolitan areas, might provide a good solution to mobile operators. Mobile network offloading, also referred to as mobile data offloading, is the use of complementary network technologies to deliver mobile data traffic originally planned for transmission over cellular networks (Han, Hui, Kumar, Marathe, Shao, & Srinivasan, 2011). This article focuses on local area networks as a complementary network technology, defining the so-called wide-to-local area offloading. The main technologies for wide-to-local area offloading are 3GPP femtocells and IEEE WiFi. Fuxjager, Fischer, Gojmerac, and Reichl (2010) provide a comparison of licensed-band femtocell versus unlicensed WiFi technologies. Other studies show that deploying multiple wireless networks including WiFi in metropolitan and city areas is an effective way of traffic offloading (Dimatteo, Hui, Han, & Li, 2011; Fuxjager, Gojmerac, Fischer, & Reichl 2011; Han, Hui, & Srinivasan, 2010; Lee, Rhee, Lee, Chong, & Yi, 2010; Yongmin, Hyun Wook, Jae-yoon, Hyun-chul, & Silvester, 2011).